This invention is directed to apparatus and methods for conveying varying size particulate material through a conduit, such as, a pipe or hose, over long distances; more particularly, to apparatus and methods that convey material in a pneumatic material handling device.
Pneumatic conveying systems for transporting material through a conduit have been in use for years and are well known in the art. Over the years the designs of these systems have changed to provide for greater efficiency in operational cost and labor. For instance, early systems utilized belt driven conveyors to transport materials from an input hopper to a mixing chamber. Unfortunately, these systems were inefficient in that the belt drives experienced many problems, such as wearing and breakage. Due, in part, to problems experienced with belt systems, pneumatic conveying systems were developed.
Generally, pneumatic conveying systems include a feed mechanism, such as, an auger, for transporting the material to a mixing chamber. In the mixing chamber, the material is entrained in pressurized air which is supplied into the mixing chamber through jets or air inlets. In some systems, the material and air are mixed and accelerated in an accelerating device, such as, a venturi pipe, which is connected to the mixing chamber. The accelerated mixture is then transported out of the venturi pipe and into a conduit which conveys the materials to a specified destination. Typically, conventional pneumatic conveying systems can transport material up to about 1,000 feet. The limited distance the material can be conveyed is due, in part, to the operating pressure of the system and the instability of the material flow in the conduit.
Many other problems also exist with pneumatic conveying systems. For example, if excessive pressure builds up in the conduit, e.g., from a blockage in the conduit, gas and product back flow into the hopper. This back flow is known as xe2x80x9cblowbackxe2x80x9d. Further, as the material travels through the conveying conduit, in earlier designs, and current designs, it strikes the walls of the conduit. This not only damages the walls of the conduit, but damages the material as well. Thus, problems of erosion of equipment and attrition of product are also present. Finally, many current designs incur a high cost of operation due to the high requirement of energy input to operate the system.
Many pneumatic systems have been developed to address different problems. For instance, the blowback problem, among others, was addressed in the system described in U.S. Pat. No. 4,711,607 to Wynosky et al. In the Wynosky device, a rotating auger enclosed by a cylindrical barrel transports particulate material towards the discharge end of the barrel which resides within a plenum chamber. Pressurized gas is introduced into the plenum chamber for creating a gas flow in a venturi pipe, which is coupled at one end to the plenum chamber and at its other end to a conduit used to transport the material. Measurements of the pressure differential between the plenum chamber and the conduit are used to monitor potential blowback problems. Further, this system operates at lower operating pressures than most systems, e.g., 12-15 psi. Nonetheless, this system does not achieve a sufficiently stable flow of material through the conduit, which restricts the distance over which the material can be transported, including the ability to transport the material through elevational or directional changes.
U.S. Pat. No. 5,681,132 to Sheppard, Jr. describes an on-line pumping unit designed to extend transport distances. In Sheppard, the pumping unit includes a screw conveyor assembly coupled to a laminar flow, inductor assembly. In this system, the inductor assembly forms the core of a linear accelerator apparatus used to extend transport distances. Nonetheless, this system does not teach how material can be conveyed over very long distances, such as, for example, a mile.
As shown from above, a need exists in the art for a system that requires low energy input, reduces equipment wear, reduces product degradation and can transport materials for long distances, such as, a mile. Further, a need exists for a system that can convey materials through dramatic high angle and vertical elevation and sharp directional changes. A need also exists for a system that can convey materials without plugging, and can further classify and mechanically dry materials during processing.
The instant invention is directed to a pneumatic material handling system that allows the formation of a strong laminar flow of materials and air surrounded by a boundary layer flow of air, such that long transport distances through dramatic elevation and directional changes can be achieved. The boundary layer flow of air protects the walls of the conducting conduit from assault by the conveyed materials, thereby protecting both the walls of the conduit and the conveyed material. Further, this system utilizes low pressure air to initiate the conduction of material, thereby dramatically reducing the operational costs of this system.
Preferred embodiments of the instant invention include a blower assembly, an inlet and an outlet conduit. The blower assembly supplies low pressure air to the system through the inlet, which in some preferred embodiments receives both air and the particulate material to be conveyed. The inlet is coupled to the flow developing device such that the air from the blower assembly passes into the mixing chamber.
The mixing chamber includes an outer barrel, an inner barrel and an accelerating chamber, wherein the inner barrel is disposed within the outer barrel and wherein the outer barrel is coupled to the accelerating chamber. The inner barrel of the mixing chamber can be either solid or hollow depending upon how materials are to be transported into the system. If materials are to be transported into the system entrained in air, then a solid or capped inner barrel is generally used. If materials are to be transported by an auger or screw type conveyor, then a hollow inner barrel may be utilized and the auger or screw placed within the hollow inner barrel.
Typically, the air from the blower is passed tangentially over the inlet such that the air, or air and material mixture, sets up a flow pattern that circulates and traverses the inner barrel towards the accelerating chamber. Once in the accelerating chamber, a vortex flow is formed. As the flow moves through the accelerating chamber, the flow accelerates and a boundary layer flow begins to form. The flow mixture then travels out of the accelerating chamber into the outlet conduit which is coupled to the accelerating chamber. As the air/material mixture travels down the outlet conduit, the vortex flow transforms into a laminar flow surrounded by the boundary layer flow. The mixture is then transported the length of the outlet conduit until it reaches its destination.
In operation, embodiments of this invention operate at pressures between 1-4 psi. One advantage of this lower pressure is that the operational costs are substantially reduced. A further advantage includes the reduction or substantial elimination of blowback problems.
Preferred embodiments of the instant invention are capable of transporting material flows through dramatic elevation and directional changes. One advantage of this feature is that the system can be utilized in various types of space and over varying terrain.
Embodiments of this system can be scaled to varying sizes. Advantages of varying sizes of this system include the ability to build a system in virtually any size space and allows users to more appropriately meet their needs, e.g., lower costs and lower production requirements and lower maintenance costs.
The material input into embodiments of this system are transported down the conduit pipe in a laminar flow surrounded by a boundary layer flow. An advantage of the boundary layer flow is that it protects the conduit pipe from material as it passes down the pipe and further protects the material that is being transported.
Due to high air to particle ratio in the material flow, the system can be shut down and restarted without the need to clear the lines, thereby gaining an advantage of eliminating costly maintenance and line plugging associated with traditional technologies.
Additionally, embodiments of this system do not emit combustion or chemical pollutants. At least one advantage of this feature is that the system does not adversely affect the environment.
Further, materials transported down the conduit are mechanically, not thermally dried of surface moisture. This provides the advantage of eliminating explosion hazards associated with current thermal dryers. It also surface dries materials at considerable lower energy costs than thermal dryers.
The above and other advantages of embodiments of this invention will be apparent from the following more detailed description when taken in conjunction with the accompanying drawings. It is intended that the above advantages can be achieved separately by different aspects of the invention and that additional advantages of this invention will involve various combinations of the above independent advantages such that synergistic benefits may be obtained from combined techniques.